Protective member for inner surface of chamber and plasma processing apparatus

ABSTRACT

An inner wall protection member used to protect the inner wall of a chamber of a plasma treatment apparatus which can be used stably for a long period of time by specifying properties of glass-like carbon materials, and a plasma treatment apparatus provided with the protection member. The hollow protection member for protecting the inner wall of a plasma processing chamber is integrally formed of glass-like carbon materials with a volume resistivity of 1×10 −2  Ω·cm or less and a thermal conductivity of 5 W/m·K or more. The protection member preferably has a thickness of 4 mm or more and the average surface roughness (Ra) of the inside of the hollow structure is preferably 2.0 μm or less. The plasma processing apparatus is configured so that the inner wall protection member having the above characteristics is arranged along the inner wall of the chamber of the plasma processing apparatus, wherein the inner wall of the chamber and the protection member are electrically connected and the chamber is grounded.

TECHNICAL FIELD

The present invention relates to an inner wall protection member used toprotect the inner wall of a chamber of a plasma processing apparatus,such as a plasma etching apparatus and a plasma CVD apparatus, forprocessing a silicon wafer in the fabrication of semiconductor devicessuch as ICs and LSIs, and to a plasma processing apparatus provided withthe protection member.

BACKGROUND ART

A plasma processing apparatus used for plasma etching has upper andlower electrodes placed in a plasma processing chamber so as to faceeach other at a predetermined interval. Plasma is generated bydischarging a reactive gas such as CF₄, CHF₃, Ar, and O₂ from orificesin the upper electrode and applying high-frequency electric power to thelower and upper electrodes. A silicon wafer or the like is placed on thelower electrode and is etched utilizing the plasma.

As a material for the electrodes, aluminum, graphite, glass-like carbon,silicon, and the like are used. As a material for the inner wall of theplasma processing chamber, aluminum, alumina in which the surface ofaluminum is oxidized, and the like are used.

The inner wall of the plasma processing chamber is chemically eroded andgenerates dust, whereby the inner wall is worn out. The dust adheres tothe surface of the wafer and this results in a defective wafer, therebydecreasing the yield. Moreover, the chamber tends to be damaged earlier.To deal with this problem, a protection member is provided on the innerwall of the plasma processing chamber to prevent the inner wall frombeing worn out due to plasma.

Japanese Patent Application Laid-open No. 9-275092 discloses a plasmaprocessing apparatus having a chamber in which a substrate to beprocessed is installed, a pump used to exhaust the inside of thechamber, electrodes for generating plasma using processing gasintroduced into the chamber thereby irradiating the plasma to thesubstrate, a replaceable protection wall provided along the inner wallof the chamber with a predetermined opening therebetween, and a coolingmeans for introducing cooling gas into the opening to prevent thetemperature of the surface of the protection wall from increasing due toheat generated in the chamber.

The Japanese Patent Application Laid-open No. 9-275092 relates to astructure for cooling the protection wall provided in the chamber of theplasma processing apparatus, wherein the protection wall is caused toabsorb polymers represented by C_(x)F_(y) produced during plasmaformation, thereby preventing the polymer from adhering to other areasof the chamber. Since this protection wall is easily replaced, theprocessing chamber can be efficiently cleaned. Moreover, since theincrease in the temperature due to plasma of the surface of theprotection wall can be prevented, stable processing is achieved.

Japanese Patent Application Laid-open No. 9-289198 discloses a plasmaprocessing apparatus with a plasma processing chamber having electrodesfor generating plasma, wherein at least the surface of the plasmaprocessing chamber is formed of glass-like carbon in the area exposed toplasma excluding the electrodes. The Japanese Patent ApplicationLaid-open No. 9-289198 also discloses a protection member for a plasmaprocessing apparatus which is arranged in a plasma processing chamberprovided with two electrodes for generating plasma, in which a plasmaregion is formed between the electrodes. The protection member isarranged so as to cover the plasma region between the electrodes, and atleast the surface thereof facing the plasma region is formed ofglass-like carbon.

According to the Japanese Patent Application Laid-open No. 9-289198,since the surface of the plasma processing chamber is formed ofglass-like carbon in the area exposed to plasma, corrosion and wear dueto plasma can be reduced. Moreover, the chamber can be used for a longerperiod of time due to low generation of particles (dust). Furthermore,contamination of the product to be processed due to dust can beprevented.

However, since plasma resistance of glass-like carbon materials variesdepending on the properties thereof, such materials must beappropriately selected to obtain suitable performance as an inner wallprotection member.

DISCLOSURE OF THE INVENTION

The present inventors have connected extensive studies on the propertiesof glass-like carbon materials suitably used for an inner wallprotection member used to protect the inner wall of a chamber of aplasma processing apparatus. As a result, the present inventors havefound that the glass-like carbon materials exhibit superior plasmaresistance, generate only a small amount of dust, and are capable ofgenerating and maintaining stable plasma. This finding has led to thecompletion of the present invention.

Specifically, an object of the present invention is to provide an innerwall protection member used to protect the inner wall of a chamber of aplasma processing apparatus which can be used in a stable manner over along period of time, by specifying the properties of glass-like carbonmaterials, and a plasma processing apparatus provided with theprotection member.

The inner wall protection member according to the present invention hasa hollow structure and is integrally formed of glass-like carbonmaterials having a volume resistivity of 1×10⁻² Ω·cm or less and athermal conductivity of 5 W/m·K or more. The protection memberpreferably has a thickness of 4 mm or more and the inner surface thereofpreferably has an average surface roughness (Ra) of 2.0 μm or less. Thehollow structure used herein includes a cylindrical shape and acylindrical shape with a hole or groove formed therein. In addition, thehollow structure includes a hollow prism in addition to a cylindricalshape.

The plasma processing apparatus according to the present invention has achamber and a hollow inner wall protection member integrally formed ofglass-like carbon materials having a volume resistivity of 1×10⁻² Q·cmor less and a thermal conductivity of 5 W/m·K or more, of which thethickness is preferably 4 mm or more and the inner surface has averagesurface roughness (Ra) of preferably 2.0 μm or less, wherein the innerwall of the chamber and the protection member are electrically connectedand the chamber is grounded.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a plasma processing apparatus, and

FIG. 2 shows an inner wall protection member which is electricallyconnected with a chamber at the bottom thereof.

BEST MODE FOR CARRYING OUT THE INVENTION

Glass-like carbon materials are unique hard carbon substances having afine hyaline structure. The substances are macroscopically nonporous andhave a three-dimensional reticulated structure. The glass-like carbonmaterials excel in chemical stability, gas impermeability, abrasionresistance, surface smoothness, and solidity, in comparison with othercarbon materials, and contain only a small amount of impurities.

In the present invention, glass-like carbon materials having a volumeresistivity of 1×10⁻² Ω·cm or less and a thermal conductivity of 5 W/m·Kor more is processed into a inner wall protection member with anintegral hollow structure. Specifically, an opening for inserting andremoving a wafer, an opening for monitoring, a groove for an exhausttube, and the like are formed in the glass-like carbon materials tofabricate a protection member with an integral structure. The protectionmember preferably has a thickness of 4 mm or more and the inner surfacethereof preferably has average surface roughness (Ra) of 2.0 μm or less.

If the volume resistivity exceeds 1×10⁻² Ω·cm, it is difficult togenerate appropriate plasma due to the difference between the potentialof the inner surface of the protection member and the groundedpotential. If the thermal conductivity is less than 5 W/m·K, thedifference in temperature between the inner surface of the protectionmember and the processing container which controls the temperature ofthe inner surface of the protection member increases, thereby requiringa longer period of time for adjusting the temperature. Moreover, it isdifficult to generate stable plasma due to nonuniform temperaturedistribution. If the protection member has a separated structure insteadof an integral structure, it is difficult to generate stable plasma dueto the uneven potential of the inner surface of the protection member.

The protection member preferably has a thickness of 4 mm or more. If thethickness is less than 4 mm, electric resistance in the verticaldirection increases when the protection member is arranged in thechamber, due to the decreased lateral cross section. As a result, thepotential difference of the inner surface of the protection member inthe vertical direction increases comparatively, whereby formation ofappropriate plasma becomes difficult. The thickness is still morepreferably 8 mm or more in order to improve durability.

The average surface roughness (Ra) of the inner surface of the hollowprotection member is preferably 2.0 μm or less. The inner surface of theprotection member is gradually worn out by the reaction with corrosivegas during plasma processing. If the average surface roughness (Ra)exceeds 2.0 μm, the inner surface of the protection member may fall offas particles depending on wear conditions. In addition, since thesurfaces of the opening for inserting and removing a wafer, the openingfor monitoring, the groove for an exhaust tube, and the like are alsoworn out during plasma processing, the average surface roughness (Ra) ispreferably 2.0 μm or less.

The plasma processing apparatus of the present invention has a chamberand an inner wall protection member with an integral hollow structureformed of glass-like carbon materials having the above characteristicswhich is arranged along the inner wall of the chamber, wherein the innerwall of the chamber and the protection member are electricallyconnected, with the chamber being grounded. If the inner wall of thechamber and the protection member are not electrically connected and thechamber is not grounded, stable, uniform plasma processing becomesdifficult due to unstable plasma. The electrical connection between theinner wall of the chamber and the protection member can be achieved byremoving an aluminum oxide layer formed on the surface of the inner walland allowing the bottom of the protection member to directly contact thealuminum material.

The glass-like carbon materials for forming the inner wall protectionmember of the present invention are manufactured as follows. In order toobtain high-density, high-purity glass-like carbon materials, purifiedphenol, furan, or polyimide thermosetting resins or blended resins ofthese having a carbon residual rate of 40% or more are used as rawmaterials. These raw material resins, either in the form of powder orliquid, are molded using an appropriate molding method such as diemolding, injection molding, and cast molding depending on the type ofresin to form a hollow molded product. The molded product is then curedat 100-250° C. in air. The cured product is filled in a graphitecrucible, or a graphite plate carrying the molded product thereon isinstead in an electric furnace or lead hammer furnace, and carbonized at800° C. or more in a nonoxidizing atmosphere such as nitrogen or argonto obtain glass-like carbon materials.

The carbonized glass-like carbon materials are placed in a vacuumfurnace of which the atmosphere is replaceable and hyper-purified byheating at 1500° C. or more in a stream of halogen purification gas suchas chlorine gas. The hyper-purified glass-like carbon materials aremachined using a hard tool such as a diamond tool and the inner surfacethereof is ground to obtain the inner wall protection member for achamber of the present invention.

The present invention will be described in more detail by examples andcomparative examples.

EXAMPLES 1-3 AND COMPARATIVE EXAMPLES 1-3

A liquid phenol-formaldehyde resin (“PR940” manufactured by SumitomoDurez Co., Ltd.) was filled in a mold made of polypropylene. The resinwas degassed under reduced pressure of 10 Torr or less for 3 hours. Theresin was put into an electric oven at 80° C. and allowed to stand for 3days to obtain cylindrical molded product. The molded product wasremoved from the mold and was cured by heating at 100° C. for 3 days,130° C. for 3 days, 160° C. for 3 days, and 200° C. for 3 days,respectively. The cured product was calcined and carbonized in anelectric furnace at a temperature rising rate of 3° C./hr and heatingtemperature of 1000° C. in a nitrogen atmosphere.

The cured product was then hyper-purified in a vacuum furnace of whichthe atmosphere is replaceable while changing the heating temperature.

The glass-like carbon materials with different characteristics thusobtained were machined using a diamond tool and the inner surfacesthereof were ground to obtain hollow inner wall protection members withdifferent surface roughness and thicknesses.

These inner wall protection members 2 were placed on the inner wall of aplasma processing chamber 1 shown in FIG. 1. The plasma processingchamber 1 made of aluminum of which the surface was oxidized wasgrounded. As shown in FIG. 2, which is an enlarged view of a portion “P”in FIG. 1, the inner wall protection member 2 was electrically connectedwith the plasma processing chamber at a bottom 101. The aluminum oxidelayer on the surface of the plasma processing chamber was removed in thearea in contact with the bottom 101. The projection of the bottom 101 ofthe inner wall protection member 2 was secured using an aluminum member102 of which the surface was oxidized. Because of this, the inner wallprotection member 2 was adequately connected at the bottom. A screwcover 103 was installed on a screw of the aluminum member 102 to preventcorrosion due to plasma.

A semiconductor wafer 3 was secured on a lower electrode 5 of the plasmaprocessing chamber 1 using an electrostatic chuck 4. A high-frequencypower supply (for example, 800 kHz) 11 was connected to the lowerelectrode 5. The lower electrode 5 was placed at the bottom of theplasma processing chamber 1 on an insulator 6. An upper electrode 7 waselectrically connected with a conductor 8, and a high-frequency powersupply (for example, 27.12 MHz) 12 was connected with the conductor 8.The conductor 8 and the plasma processing chamber 1 were arranged withan insulator 9 therebetween.

C₄F₈, O₂, and Ar were introduced from the top of the upper electrode 7to the inside of the plasma processing chamber as processing gas. AnSiO₂ film of the wafer 3 is etched using the plasma generated byapplying high-frequency electric power from the upper and lowerelectrodes. The amount of dust and uniformity on the surface of waferswas measured after etching 100 sheets of wafers. The results are shownin Table 1. The surface uniformity is an index indicating the uniformityof the etching at the center and the edge of the wafer. The surfaceuniformity is calculated according to the following formula, providedthat an etching rate at the center of the wafer is “A” and that at theend is “B”. This is the proportion (in percentage) of the differencebetween the etching rate of the center and the end of the wafer in theaverage etching rate. The larger the absolute value of the surfaceuniformity, the less uniform the etching, and the smaller the absolutevalue, the more uniform the etching. In this measurement, wafers with adiameter of 200 mm were used.${\pm \frac{{A - B}}{A + B}} \times 100\quad (\%)$

TABLE 1 Hyper-purification Volume Thermal Average surface Dust Surfacetemperature resistivity conductivity Thickness roughness generationuniformity Example No. (° C.) (10⁻² Ω · cm) (W/m · K) (mm) Ra (μm)(number) (±%) Example 1 2500 0.38 10.0 4.5 1.2 9 1.8 2 2200 0.45 8.0 5.00.5 7 2.1 3 1800 0.65 7.5 5.0 0.15 4 2.8 Comparative Example 1 1200 1.853.5 5.0 0.9 8 4.2 2 1600 1.15 4.0 3.0 0.7 10 4.4 3 1700 1.05 4.5 5.0 7.8102 3.6

As is clear from Table 1, the inner wall protection member in theexamples which were formed of the glass-like carbon materials having theproperties of the present invention generated a small amount of dust andexhibited etching uniformity on the surface in comparison with thecomparative examples. The present invention can be applied to an LCDetching apparatus by forming the protection member as a prism. In theabove examples, high-frequency electric power is applied to both theupper and lower electrodes. High-frequency electric power may be appliedto only the upper electrode, and the lower electrode and chamber may begrounded. Alternatively, high-frequency electric power may be applied toonly the lower electrode, and the upper electrode and chamber may begrounded.

INDUSTRIAL APPLICABILITY

As described above, the inner wall protection member formed of theglass-like carbon materials having specific properties of the presentinvention and the plasma processing apparatus provided with theprotection member exhibit superior plasma resistance and ensure stableplasma processing for a long period of time.

What is claimed is:
 1. A hollow protection member for protecting theinner wall of a plasma processing chamber of a plasma processingapparatus, which is integrally formed of glass-like carbon materialshaving a volume resistivity of 1×10⁻² Ω·cm or less and a thermalconductivity of 5 W/m·K or more.
 2. The protection member according toclaim 1, having a thickness of 4 mm or more.
 3. The protection memberaccording to claim 1, of which the inner surface has average surfaceroughness (Ra) of 2.0 μm or less.
 4. A plasma processing apparatuscomprising a chamber and the inner wall protection member according toclaim 1 which is arranged along the inner wall of the chamber, whereinthe inner wall of the chamber and the protection member are electricallyconnected, with the chamber being grounded.
 5. The plasma processingapparatus according to claim 4, wherein the inner wall of the chamberand the protection member are electrically connected at the bottom ofthe protection member.